Protective helmets having hard outer shells for use in various military, industrial or other applications are well known in the art. In such helmets, it is generally desirable to provide a resilient liner assembly between the outer shell and the wearer's head to help absorb shock. While straps or similar elements have customarily been used in the past for this purpose, they must be adjustable to accommodate various head sizes, resulting in some wobbling from front to back or from side to side.
Various proposals for custom-fitted liner assemblies have been suggested in an attempt to overcome this defect. According to one known method of making a custom-fitted helmet, disclosed in Morton U.S. Pat. No. 3,882,546, the outer helmet shell is spaced a suitable distance from the wearer's head and foam is injected into the region between the outer shell and an elastic layer closely overlying the wearer's head. The necessity of directly handling the foaming agent limits the utility of this method in the field.
According to another method of making a custom-fitted helmet, dislcosed in Chisum U.S. Pat. No. 4,100,320, the helmet liner is preformed with a plurality of adjacent pairs of cells respectively containing the first and second components of a foamable mixture. After the liner is placed between the helmet shell and the wearer's head, the cell partitions separating the first and second components are removed to initiate the foaming process. While this method avoids direct exposure to the liner foam, the complexity and hence expense of the preformed liner limit its practical application. Both of those methods, moreover, are one-shot procedures in that they do not permit subsequent adjustment of the liner to accommodate a different wearer or a changed head size.